Benzylhydrochlorothiazide-d5 is primarily used in analytical chemistry as an internal standard for accurate quantification in mass spectrometry. Its deuterated structure ensures minimal interference with the analyte, making it ideal for precise measurements in pharmacokinetic studies and drug metabolism research. It is also employed in the development and validation of analytical methods for detecting hydrochlorothiazide and related compounds in biological samples, such as blood or urine. Additionally, it aids in ensuring compliance with regulatory standards in pharmaceutical quality control processes.